Radiation diffractive materials based on crystalline colloidal arrays have been used for a variety of purposes. A crystalline colloidal array (CCA) is a three-dimensional ordered array of mono-dispersed colloidal particles.
Such colloidal dispersions of particles can form crystalline structures having lattice spacings that are comparable to the wavelength of ultraviolet, visible or infrared radiation. These crystalline structures have been used for filtering narrow bands of selected wavelengths from a broad spectrum of incident radiation, while permitting the transmission of adjacent wavelengths of radiation. Prior devices have been created by dispersing particles in a liquid medium, whereby the particles self-align into an ordered array. The particles are fused together by mutual polymerization or by introducing a solvent that swells and fuses the particles together.
In other uses of CCAs, an ordered array is fixed in a matrix and may be used as colorants when the fixed array diffracts radiation in the visible spectrum. Alternatively, CCAs are fabricated to diffract radiation for use as optical filters, optical switches and optical limiters. While these CCAs use constant inter-particle spacing, a CCA may function as a sensor when the inter-particle spacing varies in response to stimuli.
Recently, such sensors have been produced from hydrogels containing a CCA polymerized within the hydrogel. The polymers of the hydrogel surrounding the CCA change conformation in response to a specific external stimulus. For example, the volume of the hydrogel can change in response to stimuli, including the presence of chemicals, such as metal ions in solution and organic molecules, such as glucose, making the devices useful for chemical analysis. In CCA devices, mono-dispersed highly charged colloidal particles are dispersed in a low-ionic strength liquid media. The particles self-assemble into a CCA due to their electrostatic charges. These ordered structures diffract radiation according to Bragg's law, wherein the radiation meeting the Bragg conditions are reflected while adjacent spectral regions that do not meet the Bragg conditions are transmitted through the device.